1. Field of the Invention
The invention relates to a device for monitoring objects, in particular for monitoring industrial environments, such as paper mills and manufacturing and/or finishing processes of a paper, board or other fibrous web being carried out therein, including at least one monitoring camera or at least one sensor, which is arranged in a protective housing rotating about an axis of rotation.
2. Description of the Related Art
Monitoring devices of this type for use in rough industrial environments, such as the aforesaid paper mills, are necessary and in principle already known from the prior art. The protective housings used in this case are provided with stationary blower pipes which can be fitted and which are intended to keep the optical path between a camera and the desired object to be monitored free of dirt particles and spray mists. In very rough environments, which is to say in particular where high moisture, thermal and/or dirt loadings are present, an air knife, as it is known, is often additionally fitted to the blower pipe. This air knife improves the maintenance of the cleanliness of the interior of the blower pipe. This housing system is known in specialist paper sector circles as the “WebView System from the Papertech Company”.
However, experience has shown that, despite the provision of protective fittings, particles and droplets can penetrate into the interior of the blower pipe and can soil the camera objective or a protective glass pane fitted in front of the latter. In addition, the aforementioned device keeps only the optical path between camera and object free but not the protective housing itself. Deposits of dirt on the exterior of the housing constitute a potential hazard for specific applications. For instance, if a monitoring camera is to be fitted above the moving paper web in a paper mill, then lumps formed on the housing could be detached, fall onto the paper web and cause a web break, which is associated with a stoppage of the machine and therefore considerable production outage. As a rule, cameras in such positions must therefore be observed continuously and cleaned at regular intervals. Firstly, this results in considerable expenditure on maintenance; secondly, as a result, the area of application is limited only to points which are easily accessible. In addition, unsupervised continuous operation of the camera is not possible in this case.
A device having a self-cleaning protective housing is disclosed by WO-A1-2005/096091. In this document, a housing is described which is constructed in the manner of a dome and completely sealed. The housing rotates around the camera. The centrifugal force produced as a result is intended to ensure the action removing dirt or repelling dirt.
There are specific applications for which this concept described is not suitable, such as the use over a moving material web. Paper webs in modern plants are already running at a speed of up to 2000 m/min and more, for which reason the monitoring device cannot be brought close to the web, since otherwise aerodynamic effects endangering production would occur.
On the other hand, were the closed housing described to be fitted at a safe distance from the web, the optical path between camera and object could not be kept free of particles or spray mists. In addition, this type of housing is not capable of removing relatively large sticky dirt particles in the region of the axis of rotation, since the centrifugal forces are too low.
What is needed in the art is a device for monitoring objects which has a self-cleaning protective housing and permits a free optical path between camera or sensor and an object to be monitored better than hitherto and additionally can be used in continuous operation.